In order to measure acceleration, acceleration sensors can be used that are based on the spring-mass principle. In such a sensor, the deflection caused by an acceleration of an oscillating mass suspended on at least one spring element is acquired relative to a substrate that acts as a reference system. When the properties of the spring-mass system are known, the acceleration force acting thereon can be inferred from the behavior of the sensor. In the case of a capacitive acceleration sensor, the detection of an acceleration takes place for example by evaluating a change in capacitance that occurs due to a change in the distance between an electrode area of the oscillating body, which is held at a particular electrical potential, and an electrode that is situated so as to be stationary relative to the base substrate.
Acceleration sensors can be manufactured as micromechanical components. In so-called MEMS (Micro-Electro-Mechanical Systems), the mechanical components of an acceleration sensor are realized on, or from, the common semiconductor substrate, together with electrical circuits.
In capacitive sensor designs that operate according to the spring-mass principle, the detection of the deflection in the case of z-accelerations takes place using electrodes that are situated underneath or above the movable structure of the sensor. Here, only horizontally structured structures are used whose verticals are made up of almost vertical walls.
An object of the exemplary embodiments and/or exemplary methods of the present invention is to provide a micromechanically produced acceleration sensor having a construction whose functional design is compact, and that can be manufactured economically. This is achieved by an acceleration sensor as described herein, in which the sensor element and the detection electrodes are formed from a common functional layer. In addition, the object of the exemplary embodiments and/or exemplary methods of the present invention may be achieved by a method for manufacturing such a sensor as further described herein.
The exemplary embodiments and/or exemplary methods of the present invention provides an acceleration sensor that includes a first electrode structure that is stationary relative to a base substrate and a sensor element, having a first electrode area, that is capable of being deflected relative to the base substrate. Here, the sensor element is elastically coupled to the base substrate via at least one spring element, the distance between the first electrode structure and the first electrode area being changed when there is a deflection of the sensor element relative to the base substrate due to an acceleration. Here it is provided that the sensor element and the first electrode structure are realized so as to be situated at least partially one over the other within a common functional plane. Because the electrode structure and the electrode area of the sensor element are situated over or under one another, so that they have a common area of intersection in the x-y plane defined by the base substrate, a particularly compact construction is enabled.
In addition, due to the high degree of mechanical decoupling of the movable structure from layers situated above and beneath this structure, this sensor design has advantages with regard to robustness relative to external mechanical bending that can occur for example as a result of packaging. Because in the area of the sensor element the electrode structure runs at a spatial distance from the base substrate, the sensor is also decoupled to a great extent from surface charges that can occur on the substrate or on a substrate layer. Inter alia, this results in an improved zero stability of the sensor signal when there is a change of temperature.
An advantageous specific embodiment of the present invention provides a sensor element that is formed from a first and a second partial layer of the functional layer, the first electrode area and the first electrode structure, or a part of the second electrode structure corresponding to the second electrode area, each being formed from different sub-layers of the common functional layer. With the aid of the two-part design of the functional layer, the vertical structuring of the sensor components can be realized in a particularly simple manner.
Another advantageous specific embodiment provides that the sensor element includes a second electrode area that corresponds to a second electrode structure, which is stationary relative to the base substrate, in such a way that a deflection of the sensor element relative to the base substrate also causes a change in the distance between the second electrode structure and the second electrode area. Here, the second electrode area is formed from one of the two sub-layers of the overall functional layer, while the second electrode structure, or the part of the second electrode structure corresponding to the second electrode area, is formed from the other of the two sub-layers. With the aid of the second electrode structure, a differential, and thus also more precise, evaluation of the changing capacitance can be realized. If the first and the second electrode structure are situated on both sides of the spring element as two sub-electrodes of a single detection electrode, in this way it is also possible to compensate undesired movements, such as for example spurious oscillations, of the sensor element in the z direction.
In another specific embodiment of the present invention, the sensor element is realized in the form of a rocker that has two wings having an asymmetrical distribution of mass, and that is coupled rotatably to the base substrate via two spring elements fashioned as torsion webs. This sensor design enables a differential evaluation of the change in capacitance caused by a deflection of the seismic mass. An additional mass situated on one of the two wings enables the sensitivity of the sensor to be set.
Another advantageous specific embodiment of the present invention provides a sensor element that is fashioned in the form of a trampoline, having four wings connected to one another by respective webs. Between the wings there is situated a spring element that runs from the respective web to a central fastening base. In addition, the wings have an essentially symmetrical mass distribution. The trampoline-type sensor design enables a directional detection of the acceleration.
According to another advantageous specific embodiment of the present invention, it is provided that the spring elements are formed from the first and/or second sub-layer. In this way, the spring strength of the spring elements used can be varied between at least two levels, in a particularly simple manner.
In addition, the exemplary embodiments and/or exemplary methods of the present invention provides a method for manufacturing such an acceleration sensor in which a first sub-layer of a functional layer is deposited on a first sacrificial layer situated on a base substrate. The first sub-layer is then structured in order to produce a first plane of a sensor element and a first electrode structure, spatially separate therefrom. Subsequently, a second sacrificial layer is deposited on the first functional layer in the area of the first electrode structure, and a second sub-layer of the functional layer is then in turn deposited on this second sacrificial layer. The second sub-layer is structured in order to produce a second plane of the sensor element. Finally, the two sacrificial layers are removed. Through the use of the two sub-layers and the two sacrificial layers, the movement sensor can be produced using currently standard methods. In this way, the sensor manufacture can be incorporated into existing process sequences relatively easily.
In the following, the exemplary embodiments and/or exemplary methods of the present invention is explained in more detail on the basis of Figures.